There is an unmet need for the development of instruments and technologies that would permit fully integrated (i.e., sample-in to results-out) focused nucleic acid analysis, defined as the rapid identification (by nucleic acid sequencing or fragment sizing) of a subset of a given human, animal, plant, or pathogen genome. Focused nucleic acid sequencing will enable end-users to make real-time clinical, forensic, or other decisions. For example, many common human diseases can be diagnosed based on less than 1000 base pairs of DNA sequence, orders of magnitude less than required to generate a complete human genome. Similarly, precise determination of the sizes of sets of less than 20 specific DNA fragments generated by short tandem repeat analysis is sufficient to identify a given individual. Depending on the application, focused nucleic analysis can be performed in a variety of settings, including hospital laboratories, physician's offices, the bedside, or, in the case of forensic or environmental applications, in the field.
There are several unmet needs for improved DNA sequencing and fragment sizing systems. First, there is an unmet need for DNA sequencing and fragment sizing instruments that are easy to use and do not require highly trained operators. Second, there is an unmet need for systems that eliminate all manual processing. As a result, only minimal operator training would be required and the system could be readily operated by individuals constrained by challenging environments such as would be encountered, for example, by a first responder wearing a haz-mat suit.
Third, there is an unmet need for ultrafast analysis that does not sacrifice the need for complete, accurate, and reliable data. For human identification applications, an appropriate time to result is 45 minutes or less, well under the days to weeks required using conventional technology. For clinical applications such as sequencing infectious agents to determine an appropriate treatment regimen, 90 minutes or less is a reasonable time to answer, allowing treatment with antibacterial and antiviral medications to be initiated shortly after a patient's arrival in an emergency room. Regardless of application, there is an unmet need to generate actionable data in real time. A short time to answer also allows a concomitant increase in sample throughput.
Fourth, there is an unmet need for miniaturization. Many DNA analysis systems require an entire laboratory and related support. For example, the high throughput Genome Sequencer FLX (Roche Diagnostics Corp, Indianapolis, Ind.) DNA sequencing system requires only a benchtop for installation but a large laboratory to perform the required library construction. Miniaturization is important both for laboratory and point-of-care use as well as field operation. It is also important for cost reduction per sample.
Fifth, there is an unmet need for ruggedization. For many applications, particularly those in forensics, the military, and homeland defense, the DNA analysis instrument must be operable in the field. Accordingly, the instrument must be capable of transport whether carried on a soldier's back, driven in a police vehicle, or dropped from a helicopter into a battlefield. Similarly, the instrument must be able to withstand and function under environmental extremes, including temperature, humidity and airborne particulates (e.g., sand).
Sixth, there is an unmet need for systems that can accept multiple sample types and perform highly multiplexed analyses in parallel. For most applications, capability of analysis of DNA from a single sample type in a singleplex reaction is not acceptable to perform meaningful DNA analysis.
Developers of microfluidics (also referred to as micro total analysis systems (μTAS) or lab-on-a-chip technologies, see, Manz et al., Sens. Actuators B 1990, 1, 244-248) who are seeking to condense complex series of laboratory manipulations onto biochips have recognized certain of these unmet needs, but to date, have been unable to design integrated biochips and instruments that perform all of the biochemical and physical processes necessary or desirable to allow microfluidic nucleic acid analysis to address these needs. As a result, focused nucleic acid analysis has not entered into widespread use in society today.
The development of microfluidic systems involves the integration of microfabricated components, such as microscale separations, reactions, microvalves and pumps and various detection schemes into fully functional devices (see, e.g., Pal et al., Lab Chip 2005, 5, 1024-1032). Since Manz et al. (supra), demonstrated capillary electrophoresis on a chip in the early 1990's, others have sought to improve upon it. Several groups have demonstrated integration of DNA processing functionality with biochip separation and detection. Integrated devices in a glass-PDMS (polydimethylsiloxane) hybrid structure have been reported (Blazej et al., Proc Natl Acad Sci USA 2006, 103, 7240-5; Easley et al., Proc. Natl. Acad. Sci. USA 2006, 103, 19272-7; and Liu et al., Anal. Chem. 2007, 79, 1881-9). Liu coupled multiplex polymerase chain reaction (PCR), separation and four dye detection for human identification by short tandem repeat (STR) sizing. Blazej coupled Sanger sequencing reaction, Sanger reaction cleanup, electrophoretic separation and four dye detection for DNA sequencing of pUC18 amplicon. Easley coupled solid phase extraction of DNA, PCR, electrophoretic separation and single color detection to identify the presence of bacterial infection in blood. An integrated silicon-glass device coupling PCR, electrophoretic separation and single color detection was demonstrated by Burns (Pal, 2005, Id.). A hybrid device coupling a glass-PDMS portion for PCR to a poly(methyl methacrylate) (PMMA) portion for electrophoretic separation and single color detection for identifying the presence of bacteria DNA was reported by Huang (Huang et al., Electrophoresis 2006, 27, 3297-305).
Koh et al., report a plastic device that coupled PCR to biochip electrophoretic separation and single color detection for identifying the presence of bacterial DNA (Koh et al., Anal. Chem. 2003, 75, 4591-8). A silicone based device that couples DNA extraction, PCR amplification, biochip electrophoretic separation and single color detection was reported by Asogawa (Asogowa M, Development of portable and rapid human DNA Analysis System Aiming on-site Screening, 18th International Symposium on Human Identification, Poster, Oct., 1-4, 2007, Hollywood, Calif., USA). U.S. Pat. No. 7,332,126 (Tooke et al.) describes the use of centrifugal force to effect microfluidic operations required for nucleic acid isolation and cycle sequencing. However, this approach is based on small sample volumes, (those of the order of one to a few μL). As a result, the device is not useful for the processing of large samples for the isolation and analysis of nucleic acids, especially in highly parallel fashion, because the fluid samples must be applied to the device while stationary, which is, the disc must be able to contain all the fluids required for operation prior to centrifugation (potentially up to 100 s of mL for a highly-parallel device). Secondly, the device is limited to sample preparation and cycle sequencing, of bacterial clones (e.g., plasmid DNA).
There are several deficiencies in those devices that attempt to integrate DNA processing with biochip electrophoretic separation. First, detection is limited by either information content per assay (most use single color detectors although some have up to four color detection systems) or throughput (single sample or two sample capability). Second, these devices do not represent complete sample-to-answer integration, e.g., Blazej's device requires off-board amplification of template DNA prior to cycle sequencing, while others use samples that require pre-processing of some sort (e.g., Easley and Tooke require lysis of the sample before addition). Third, some of the processing choices made for these devices negatively impact time-to-answer: for example, the hybridization-based method of Blazej requires more than 20 minutes for cleanup of the cycle sequencing product. Fourth, many of these devices are fabricated in part or in-whole glass or silicon. The use of these substrates and corresponding fabrication techniques make them inherently costly (Gardeniers et al., Lab-on-a-Chip (Oosterbroeck R E, van den Berg A, Eds.). Elsevier: London, pp 37-64 (2003)) and limit them to applications where reuse of the devices must be performed; for many applications (such as human ID) this leads to the risk of sample contamination. Finally, the demonstrated technology is inappropriate for two applications, human identification via STR analysis and sequencing. For example, the Easley and Pal devices both suffer from poor resolution—much worse than a single base. Fragment sizing applications (e.g., human identification by analysis of short tandem repeat profiles) and sequencing both require single base resolution.
In addition to the limitations of the prior art with respect to microfluidic integration, problems with respect to fluorescence detection also limit the widespread application of nucleic acid analysis beyond conventional laboratory work. The most widely used commercial sequencing kits (BigDye™ v3.1 [Applied Biosystems] and DYEnamic™ ET [GE Healthcare Biosciences Corp, Piscataway, N.J.]) are based on a twenty year old detection method for four color (see, e.g., U.S. Pat. Nos. 4,855,225; 5,332,666; 5,800,996; 5,847,162; 5,847,162). This method is based on resolution of the emission signal of a dye-labeled nucleotide into four different colors, one representing each of the four bases. These four-color dye systems have several disadvantages, including inefficient excitation of the fluorescent dyes, significant spectral overlap, and inefficient collection of the emission signals. The four color dye systems are especially problematic because they limit the amount of information that can be gained from a given electrophoretic (or other) separation of sequenced products.
There is an unmet need for a system capable of achieving high information content assays in electrophoretic systems based on separation and detection of DNA fragments by both fragment size and by color (dye wavelengths). The maximum number of DNA fragments that can be distinguished by electrophoresis is determined by the readlength of the separation and the resolution of the device. The maximum number of colors that can be detected is determined in part by the availability of fluorescent dyes and the wavelength discrimination of the detection system. Current biochip detection systems are typically limited to single color, although up to 4 color detection has been reported.
STR analysis for human identification is an example of DNA fragment sizing based on color multiplexing and allows simultaneous analysis up to 16 loci (AmpFlSTR Identifiler kit; Applied Biosystems, Foster City, Calif.) and PowerPlex16 kit (Promega Corporation, Madison, Wis.). Using four or five fluorescent dyes, a single separation channel can discriminate among the sizes of the many allelic variants of each locus. Several fragment sizing applications would require more than 16 fragments to be separated and detected on a single lane. For example, the identification of pathogens by fingerprinting (i.e., the separation and detection of a large number of characteristic DNA fragments) and the diagnosis of aneuploidy by surveying the entire human genome can be accomplished by looking at several dozen or several hundred loci, respectively.
One approach to increasing the number of loci that can be detected in a single separation channel is to broaden the range of fragment sizes generated, in part by increasing the fragment sizes of additional loci. The use of longer fragments for additional loci is not ideal, however, as amplification of larger fragments is more susceptible to inhibitors and DNA degradation, leading to lower yields of longer fragments relative to shorter fragments. Furthermore, the generation of longer fragments also requires an increase in the extension time and hence, an increase in the total assay time. There is an unmet need to increasing the number of loci that can be detected in a given separation channel by increasing the number of dye colors that can be simultaneously detected.
There is an unmet need to increase the capacity of Sanger sequencing separations (and therefore decrease the cost, labor, and space of the process) by increasing the number of DNA sequences that can be analyzed in a single separation channel. In addition, in some applications, multiple DNA fragments are sequenced that generate difficult to read “mixed sequence” data; there is a need to develop an approach in that mixed sequences can be interpreted correctly.
One approach to increasing the capacity of Sanger separation channels and developing the ability to interpret mixed sequences is to increase the number of dye colors utilized in the sequencing reactions. In both DNA sequencing and fragment sizing, multiple fragments labeled with different dyes can be detected at the same time. In general, the separation between peak emission wavelengths of adjacent dyes must be large enough relative to peak width of the dyes. Accordingly, the throughput of each separation channel can, for example, be doubled by utilizing two sets of 4 dyes in two independent sequencing reactions, and combining the products, and separating them on a single channel. This methodology requires the use of a total of 8 dye colors, with the first sequence reaction using a set of 4 dye colors applied to label the dideoxynucleuotide terminators, and the second reaction another set of 4 dye colors applied to the label the terminators; each set of dye colors is independent so that no overlap in interpretation of the two sequences is possible. Using this same approach, a set of 12 dyes can be utilized to allow simultaneous analysis of the sequence of three DNA fragments in a single channel, a set of 16 dyes allows the analysis of four sequences, and so on, dramatically increasing the information capacity of Sanger separations.
The novel instruments and biochips of this application satisfy many unmet needs, including those outlined above.